The relationship between intrauterine infections and complications of pregnancy is poorly understood. Our central hypothesis is that first trimester trophoblast cells can recognize and respond to pathogens through Toll-like receptors, and that such innate immune functions of trophoblast cells may influence pregnancy outcome. Toll-like receptors (TLR) are key components of the innate immune system which recognize conserved sequences on the surface of microorganisms and trigger effector cell functions via the signaling adapter protein, MyD88. We have demonstrated that first trimester trophoblast cells express TLR-2 and TLR-4. Following ligation by gram-positive bacterial components, TLR-2 mediates apoptosis in first trimester trophoblast cells. In contrast, ligation of TLR-4 by gram-negative bacterial components induces cytokine production. Thus, we have found that trophoblast cells can mount divergent responses to different bacterial components through two distinct TLR. Our objectives are to further characterize the mechanisms by which TLR-2 and TLR-4 function in first trimester trophoblast cells and to determine their role during pregnancy. Our specific aims are to: 1. Determine the mechanisms by which TLR-2 functions in first trimester trophoblast cells 2. Determine the mechanism by which TLR-4 functions in first trimester trophoblast cells 3. Determine the regulation of TLR expression by first trimester trophoblast cells 4. Determine the effects of TLR activation on pregnancy in vivo Little is known about how trophoblast cells recognize and respond to microorganisms. The area of Toll-like receptors in pregnancy is a novel one. Therefore, it is important to understand the role of Toll-like receptors within the normal placenta. These studies will provide new insight into how trophoblast cells function in the presence of an infection and will advance our understanding of pathological conditions, such as preeclampsia, IUGR or preterm deliveries.